The uses for three-dimensional metrology are expanding rapidly. In the construction industry, there are increased demands for prompt information concerning the status of a job site. The immediate impediment to the effective use of scanning technology is the xe2x80x9cLine of Sight limitationsxe2x80x9d. If a pile of dirt is in front of an existing stationary scanner anything behind the pile invisible. There is no present ability to look over or around the obstacle. This problem also extends to the interior of buildings thereby preventing the development of as-built scans. Therefore, all such interior scans presently are 2xc2xdD images and not true 3D.
In the nuclear industry the current approach to developing interior geometry of hot cells generally involves the use of time-consuming techniques. For example, in a hot cell environment the accurate location of nozzle positions is critical for the fabrication of remotely handled piping jumpers. Because of the critical nature of the work workers cannot depend upon the accuracy of shop drawings. In addition, these areas have high levels of radioactivity thus preventing long-term exposure by workers. Surveying is impossible because of the limited space available for equipment and instruments. Photogrammetry is sometime used to develop a 3D image of hot cell areas. 3D coordinate measurements can be made from stereo pair photographs. It is a system adapted from aerial photography mapping.
In this method, a scanner reads the photographs and a computer calculates the coordinates. The use of Photogrammetry is limited in that when used in a hot cell environment the camera lenses will fog and target grids must be developed for each item needing to be surveyed. The use of target grids is untenable because the items are constantly moved by remote manipulators. The use of laser scanning devices could also be used to image the inside of the hot cell, but these suffer from the problems previously pointed out. Such as, line of sight limitations, limited field of view of a stationary laser, and the fact that lasers are not radiation hard, that is radiation causes the equipment to malfunction.
Another reference which provides laser scanning techniques but do not overcome line of sight limitations, nor hot cell contamination problems is U.S. Pat. No. 5,114,226 to Goodwin et al. which discloses a 3-dimensional vision system, comprising scanner optics, a laser head, receiver circuitry, and a control system microprocessor. The scanning optics may include a facet wheel with a galvanometer scanner.
Field discloses in U.S. Pat. Nos. 4,790,402, 4,846,297, and 4,996,468 an automated guided vehicle, comprising a laser scanner mounted on a platform. The angle of elevation of the light beam emitted by the laser scanner is controlled by a linear actuator.
U.S. Pat. No. 4,703,820 to Reinaud discloses a vehicle guidance system involving a laser beam, horizontal and vertical scanning motors, and targets. Through control of the scanning motors, the laser beam can be moved through a desired scanning pattern.
U.S. Pat. No. 4,636,846 issued to Villarreal discloses an optical scanning apparatus comprising a light source, a camera, and a conical mirror. The scanner apparatus is employable in radioactive environments.
What is needed but not provided in the prior art is an apparatus for laser scanning that has a telescoping mast and the ability to take scans at multiple positions and a method for developing a real-time 3D image and overcoming line of sight problems associated with hot cells and construction sites. Additionally, it would also be helpful to provide such features in a compact, inexpensive, and simple design. Finally, it would be helpful to have a system which works in conjunction with the global positioning system.
The inventor has overcome the problems remaining from the prior art by devising a 3-degree-of-freedom scanning device for the creation of a precise 3-dimensional stereo range image. The device employs a standard single point diode pulsed or continuous wave laser ranging system being operated in a non-cooperative target mode. The laser source and range determination electronics are located in an environmentally secure chamber at one end of a hollow telescoping nested mast and are oriented such that the outgoing laser pulse/beam is directed down the center of the hollow mast system. The mast is deployed (extended) by a precision extension mechanism to accurately determine the instant extension length of the telescoping mast. There may be two or more elements to the telescoping mast assembly. The mast system includes a displacement feedback means, which precisely determines the instant deflections and slopes of the sensor head, which is attached to the end of the furthest extended telescope tube. The sensing head is modular and is capable of being detached from the mast. In addition, the sensing head is capable of being rotated a full 360xc2x0 degrees about a longitudinal centerline of the extension mast tube by a precision encoding system which provides a real time feedback on the angular orientation of the sensing head relative to a reference position on the telescoping mast system.
The advantages of the present invention are achieved with a multi-faceted precision rotating mirror which serves to deflect the ranging laser pulse/beam towards a presumed non-cooperative target scene point. The light reflected from the target point is picked up by the rotating mirror and returned down the hollow core of the telescoping mast where it is sensed by the ranging element receiver and used to determine a total path distance from the laser source to the target. The rotating mirror may have one or more reflecting surfaces and also contains a precision encoding system means, which provides real-time feedback on the angular orientation of the mirror.
It is an object of the invention to provide a 3 degree of freedom laser scanner system.
It is another object of the invention to provide a mast mounted 3D laser scanner.
Another object of the invention is to provide a 3D laser scanner for use in radiation contaminated areas.
It is another object to provide a 3D laser scanner where the scanning head can be remotely placed in a high radiation area with the electronics located outside the contamination area.
It is yet another object to provide a 3D scanner in conjunction with a global coordinate system.
Other features and advantages of the present invention will be apparent that the following description in which the preferred embodiments have been set forth in conjunction with the accompanying drawings